Indocyanine green-enhanced fluorescence optical imaging of the hands identified signals in patients’ nails that were highly specific for psoriatic arthritis (PsA), according to a study in the Journal of the German Society of Dermatology.
“Early diagnosis of PsA poses a particular challenge,” the researchers wrote. “A novel fluorescence optical imaging technique, the Xiralite system, is very useful in this regard as it allows for visualization of microvasculature and perfusion.”
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Researchers described a pair of investigations. In the first, they analyzed extra-articular fluorescence optical signal patterns in 241 imaging sequences from 187 participants with PsA and compared them with 36 fluorescence optical sequences from 31 participants with rheumatoid arthritis, who served as control subjects. In a follow-up analysis, they evaluated 203 consecutive fluorescence optical sequences from 54 participants with PsA and 149 control subjects with various inflammatory rheumatic disorders to validate patterns identified in the primary study.
Participants with PsA demonstrated 3 different fluorescence optical signal patterns in the nails, according to the study. One pattern, called the “green nail” sign, was 97% specific for PsA in the first analysis and 87% specific for PsA in the follow-up analysis compared with controls.
“The ‘green nail’ phenomenon seems to be of particular diagnostic interest as a potential sign of impaired microcirculation of the nail bed,” the researchers wrote.
Wiemann O, Werner SG, Langer HE, Backhaus M, Chatelain R. The "green nail" phenomenon in ICG-enhanced fluorescence optical imaging—a potential tool for the differential diagnosis of psoriatic arthritis. J Dtsch Dermatol Ges. 2019;17(2):138-147.